This research proposal is to study the effects of opioids and opioid antagonists, and of prototypical and atypical antipsychotic drugs on behavior controlled by noxious stimuli and other consequent events. One major objective will be to specify the pharmacological and environmental factors responsible for the development and expression of supersensitivity to the behavioral effects of opioid antagonists. Studies will be conducted on how the development of supersensitivity is modified by the type of schedule and type of consequent event that maintains behavior, and on how developed supersensitivity alters the behavioral effects of opioids from different chemical classes. Other studies will investigate how the behavioral effects of opioid antagonists are modified by pretreatment with other drugs in supersensitive and normal subjects, and on how supersensitivity alters the antagonistic effects of opioid antagonists. Supersensitivity also will be studied in relation to the suppression of behavior by response-produced injections of opioid antagonists or by stimuli associated with injections of antagonists. A second major objective of the proposed research is to characterize the distinctive behavioral effects of prototypical and atypical antipsychotic drugs and to specify how these effects are determined by the environmental conditions that maintain or suppress behavior.